2-substituted-1,4-benzenediamine, for example 2-methoxymethyl-1,4-benzenediamine, and cosmetically acceptable salts thereof are useful as primary intermediates in oxidative hair color.
Although the diazotization route to p-phenylenediamine (PPD) is known (EP 0052511 A1), and it has been used to manufacture PPD successfully, it is similarly well-known that, although the synthesis of 2-methyl-p-phenylenediamine has been accomplished by a diazotization route on a smaller scale (Rajaganesh, Ramanathan et al; Organic Letters, 14(3), 748-751; 2012), there has been an inability to use it as an industrial route
CA 2,576,189 discloses the application of combinations of 2-methoxymethyl-1,4-benzenediamine with various couplers and primary intermediates in oxidative dyeing compositions. U.S. Pat. No. 2,273,564 discloses a process to synthesize substituted 1,4-benzenediamine compounds with a substituent on the 2 position. U.S. Pat. No. 6,648,923 B1 discloses a process to synthesize 2-methoxymethyl-1,4-benzenediamine and the salts thereof. U.S. Pat. No. 9,012,691 describes a process to prepare 2-methoxymethyl-1,4-benzenediamine and the salts thereof beginning with 5-nitro-isatoic anhydride.
The previous syntheses described above to reach 2-alkoxymethyl-1,4-benzenediamines, their derivatives, and salts thereof are not completely satisfactory. Therefore, there is a need for a simple, industrially applicable, efficient, and cost effective process for the preparation of 2-substituted-1,4-benzenediamines, a cosmetically acceptable salt thereof or mixture thereof.
The inventors have surprisingly found that at least some of these needs may be met by a process according to the present invention wherein the reaction by-product (a 2-substituted aniline) can be recycled in the process by distillation, chromatography, etc.